As an example of power semiconductor devices, there is a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) of a vertical electrode structure. To reduce on-resistance in such power MOSFET, a power MOSFET of a field plate structure in which a deep trench is formed in a drift layer and an embedded electrode is formed in the trench via an insulating film is used. The field plate structure is provided periodically in the drift layer, and a depletion layer is extended from the field plate structure in a lateral direction of the drift layer when a voltage is applied. Thereby, a high breakdown voltage is maintained. As a result, in this power MOSFET, the impurity concentration of the drift layer can be made higher than that of the conventional power MOSFET, and a low on-resistance that exceeds the material limit is realized.
On the other hand, the power MOSFET of the vertical electrode structure has a pn diode (built-in diode) formed of a base layer, a drift layer and a drain layer. To realize a high-speed built-in diode, a Schottky barrier diode (SBD) using a Shottky junction may be built into the semiconductor device.
However, when forming the Schottky barrier diode in a basic unit cell of the power MOSFET, a cell unit (period in a lateral direction of the cell) of the region where the Shottky junction is formed become larger. For the power MOSFET having the field plate structure, the longer the period in the lateral direction is, the more the on-resistance is raised. Moreover, the longer the period in the lateral direction is, the more the electric field strength at the Schottky junction is enhanced, and there is a possibility that leakage current is increased by the Schottky barrier diode.